Power decision pilot for wireless communication

ABSTRACT

Techniques for transmitting power decision pilots are described. A transmitter (e.g., a base station or a UE) may transmit a power decision pilot to indicate a transmit power level that it will use on subsequent time-frequency resources. In one design, the transmitter may determine a set of time-frequency resources to use for transmitting the power decision pilot, determine the transmit power level for the power decision pilot based on the transmit power level to use for data transmission, and transmit the power decision pilot on the set of time-frequency resources to indicate the transmit power level to use for data transmission on the subsequent time-frequency resources. A receiver (e.g., a UE or a base station) may receive power decision pilots from a set of transmitters and may estimate channel quality that the receiver can expect on the subsequent time-frequency resources based on the power decision pilots.

The present application claims priority to provisional U.S. ApplicationSer. No. 61/147,407, entitled “Power Decision Pilot Indicator Channel,”filed Jan. 26, 2009, provisional U.S. Application Ser. No. 61/147,408,entitled “Power Decision Pilot Indicator Channel,” filed Jan. 26, 2009,provisional U.S. Application Ser. No. 61/147,851, entitled “PowerDecision Pilot Indicator Channel—OFDMA,” filed Jan. 28, 2009, andprovisional U.S. Application Ser. No. 61/148,110, entitled “PowerDecision Pilot Indicator Channel—SCFDMA,” filed Jan. 29, 2009, allassigned to the assignee hereof and incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for supporting communication in a wirelesscommunication network.

II. Background

Wireless communication networks are widely deployed to provide variouscommunication content such as voice, video, packet data, messaging,broadcast, etc. These wireless networks may be multiple-access networkscapable of supporting multiple users by sharing the available networkresources. Examples of such multiple-access networks include CodeDivision Multiple Access (CDMA) networks, Time Division Multiple Access(TDMA) networks, Frequency Division Multiple Access (FDMA) networks,Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA)networks.

A wireless communication network may include a number of base stationsthat can support communication for a number of user equipments (UEs). AUE may communicate with a base station via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from thebase station to the UE, and the uplink (or reverse link) refers to thecommunication link from the UE to the base station.

A base station may transmit data and control information on the downlinkto a UE and/or may receive data and control information on the uplinkfrom the UE. On the downlink, a transmission from the base station mayobserve interference due to transmissions from neighbor base stations.On the uplink, a transmission from the UE may cause interference totransmissions from other UEs communicating with the neighbor basestations. The interference may degrade performance on both the downlinkand uplink.

SUMMARY

Techniques for transmitting power decision pilots to supportcommunication in the presence of interference are described herein. Atransmitter (e.g., a base station or a UE) may transmit a power decisionpilot to indicate a transmit power level that it will use on subsequenttime-frequency resources. A receiver (e.g., a UE or a base station) mayreceive power decision pilots from a set of transmitters and mayestimate channel quality that the receiver can expect on the subsequenttime-frequency resources based on the power decision pilots. Theestimated channel quality may be used to select a data rate for datatransmission to the receiver.

In one design, a station (e.g., a base station or a UE) may determine aset of time-frequency resources to use for transmitting a power decisionpilot. This set of time-frequency resources may comprise a set ofresource elements for at least one OFDMA symbol, or a set of resourceunits for at least one SC-FDMA symbol, or some other type of resources.The station may determine a transmit power level for the power decisionpilot based on a transmit power level to use for data transmission. Thestation may transmit the power decision pilot on the set oftime-frequency resources in a first time period to indicate the transmitpower level to use for data transmission in a second time period afterthe first time period. The station may transmit the power decision pilotat zero power if data transmission will not be sent in the second timeperiod.

The station may transmit one or more additional power decision pilots onone or more additional sets of time-frequency resources. In one design,multiple power decision pilots may be transmitted on different subbandsand may indicate the transmit power levels to use for data transmissionon these subbands. In another design, multiple power decision pilots maybe transmitted on the same subband and may indicate the transmit powerlevels to use for data transmission on different subbands. In yetanother design, multiple power decision pilots may be transmitted in thefirst time period and may indicate transmit power levels to use for datatransmission in different time periods after the first time period.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication network.

FIG. 2 shows an exemplary data transmission scheme for the downlink.

FIG. 3 shows an exemplary data transmission scheme for the uplink.

FIG. 4 shows an exemplary frame structure.

FIG. 5 shows transmission of a power decision pilot with OFDMA.

FIGS. 6A and 6B show two subframe formats for a power decision pilot.

FIGS. 7A, 7B and 7C show transmission of multiple power decision pilots.

FIG. 8 shows transmission of a power decision pilot with SC-FDMA.

FIGS. 9 and 10 show exemplary transmission of power decision pilots byfour UEs in one SC-FDMA symbol period.

FIG. 11 shows a process for transmitting a power decision pilot.

FIG. 12 shows an apparatus for transmitting a power decision pilot.

FIG. 13 shows a process for receiving power decision pilots.

FIG. 14 shows an apparatus for receiving power decision pilots.

FIG. 15 shows a block diagram of a base station and a UE.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication networks such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part ofUniversal Mobile Telecommunication System (UMTS). 3GPP Long TermEvolution (LTE) and LTE-Advanced (LTE-A) are new releases of UMTS thatuse E-UTRA, which employs OFDMA on the downlink and SC-FDMA on theuplink. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described indocuments from an organization named “3rd Generation PartnershipProject” (3GPP). cdma2000 and UMB are described in documents from anorganization named “3rd Generation Partnership Project 2” (3GPP2). Thetechniques described herein may be used for the wireless networks andradio technologies mentioned above as well as other wireless networksand radio technologies. For clarity, certain aspects of the techniquesare described below for LTE, and LTE terminology is used in much of thedescription below.

FIG. 1 shows a wireless communication network 100, which may be an LTEnetwork or some other wireless network. Wireless network 100 may includea number of evolved Node Bs (eNBs) 110 and other network entities. AneNB may be a station that communicates with the UEs and may also bereferred to as a base station, a Node B, an access point, etc. Each eNB110 may provide communication coverage for a particular geographic area.In 3GPP, the term “cell” can refer to a coverage area of an eNB and/oran eNB subsystem serving this coverage area, depending on the context inwhich the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell,a femto cell, and/or other types of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell, e.g.,UEs in a Closed Subscriber Group (CSG). In the example shown in FIG. 1,eNBs 110 a, 110 b and 110 c may be macro eNBs for macro cells 102 a, 102b and 102 c, respectively. eNB 110 x may be a pico eNB for a pico cell102 x. eNB 110 y may be a femto eNB for a femto cell 102 y. An eNB maysupport one or multiple (e.g., three) cells.

Wireless network 100 may be a homogeneous network that includes eNBs ofthe same type, e.g., only macro eNBs or only femto eNBs. Wirelessnetwork 100 may also be a heterogeneous network that includes eNBs ofdifferent types, e.g., macro eNBs, pico eNBs, femto eNBs, etc. Thesedifferent types of eNBs may have different transmit power levels,different coverage areas, and different impact on interference inwireless network 100. For example, macro eNBs may have a high transmitpower level (e.g., 20 Watts) whereas pico eNBs and femto eNBs may have alower transmit power level (e.g., 1 Watt).

Wireless network 100 may be a synchronous network or an asynchronousnetwork. For a synchronous network, the eNBs may have similar frametiming, and transmissions from different eNBs may be approximatelyaligned in time. For an asynchronous network, the eNBs may havedifferent frame timing, and transmissions from different eNBs may not bealigned in time. The techniques described herein may be used for bothsynchronous and asynchronous networks.

A network controller 130 may couple to a set of eNBs and may providecoordination and control for these eNBs. Network controller 130 maycommunicate with eNBs 110 via a backhaul. eNBs 110 may also communicatewith one another, e.g., directly or indirectly via wireless or wirelinebackhaul.

UEs 120 may be dispersed throughout wireless network 100, and each UEmay be stationary or mobile. A UE may also be referred to as a terminal,a mobile station, a subscriber unit, a station, etc. A UE may be acellular phone, a personal digital assistant (PDA), a wireless modem, awireless communication device, a handheld device, a laptop computer, acordless phone, a wireless local loop (WLL) station, etc. A UE may beable to communicate with macro eNBs, pico eNBs, femto eNBs, etc. In FIG.1, a solid line with double arrows indicates desired transmissionsbetween a UE and a serving eNB, which is an eNB designated to serve theUE on the downlink and/or uplink. A dashed line with double arrowsindicates interfering transmissions between a UE and a neighbor eNB.

A UE may be within the coverage of multiple eNBs. One of these eNBs maybe selected to serve the UE. The serving eNB may be selected based onvarious criteria such as received power, pathloss, signal-to-noise ratio(SNR), etc.

A UE may operate in a dominant interference scenario in which the UE mayobserve high interference from and/or may cause high interference to oneor more neighbor eNBs. A dominant interference scenario may occur due torestricted association. For example, in FIG. 1, UE 120 y may be close tofemto eNB 110 y and may have high received power for eNB 110 y. However,UE 120 y may be unable to access femto eNB 110 y due to restrictedassociation and may then connect to macro eNB 110 c with lower receivedpower. UE 120 y may then observe high interference from femto eNB 110 yon the downlink and may also cause high interference to eNB 110 y on theuplink.

A dominant interference scenario may also occur due to range extension,which is a scenario in which a UE connects to an eNB with lower pathlossand lower SNR among all eNBs detected by the UE. For example, in FIG. 1,UE 120 x may detect macro eNB 110 b and pico eNB 110 x and may havelower received power for eNB 110 x than eNB 110 b. Nevertheless, it maybe desirable for UE 120 x to connect to pico eNB 110 x if the pathlossfor eNB 110 x is lower than the pathloss for macro eNB 110 b. This mayresult in less interference to the wireless network for a given datarate for UE 120 x.

In an aspect, a power decision pilot (PDP) may be used to supportcommunication in the presence of high interference. A power decisionpilot may also be referred to as a power decision pilot channel(PDPICH), a power decision pilot indicator channel, a power decisionreference signal, a resource quality indicator reference signal(RQI-RS), etc. Pilot is a transmission that is known a priori by atransmitter and a receiver and may also be referred to as a referencesignal, training, etc. A power decision pilot is a pilot indicative of atransmit power level to be used on subsequent time-frequency resources.A transmitter may transmit a power decision pilot to indicate thetransmit power level that it will use on subsequent time-frequencyresources. A receiver may receive power decision pilots from a set oftransmitters and may estimate the SNR (or the channel and interferenceconditions) that the receiver can expect on the subsequenttime-frequency resources. The estimated SNR may be used to select a datarate for data transmission to the receiver on the subsequenttime-frequency resources.

FIG. 2 shows a design of a downlink data transmission scheme 200 thatuses power decision pilots. A serving eNB may have data to send to a UEand may have knowledge that the UE is observing high interference on thedownlink. For example, the serving eNB may receive pilot measurementreports from the UE, and the reports may indicate and/or identify strongneighbor eNBs for the UE. The serving eNB may send a PDP trigger to theUE at time T₀. The UE may receive the PDP trigger and, in response, maysend a PDP request at time T₁ to ask the neighbor eNBs to transmit powerdecision pilots. The PDP trigger and/or the PDP request may convey thepriority of the trigger or request, a target interference level for theUE, and/or other information

A neighbor eNB may receive the PDP request from the UE. The neighbor eNBmay determine a transmit power level P_(DATA) that it will use onsubsequent time-frequency resources based on various factors such as itsbuffer status, the priority of the PDP request, a target interferencelevel, etc. The neighbor eNB may transmit a power decision pilot at apower level of P_(PDP) at time T₂. P_(PDP) may be equal to P_(DATA) ormay be a scaled version of P_(DATA).

The serving eNB may periodically transmit a pilot (e.g., at a fixedtransmit power level), which may be used by the UEs to estimate thechannel conditions for the downlink from the serving eNB. Although notshown in FIG. 2 for simplicity, the serving eNB may also transmit apower decision pilot, which may be used by the UEs to estimate thechannel conditions on the downlink from the serving eNB.

The UE may receive power decision pilots from all neighbor eNBs as wellas the pilot from the serving eNB. The UE may estimate SNR based on thereceived pilots. The power decision pilots may allow the UE to moreaccurately estimate SNR. The UE may determine channel quality indicator(CQI), which may comprise one or more SNR estimates, one or more datarates, one or more modulation and coding schemes (MCSs), etc. The UE maysend the CQI to the serving eNB at time T₃.

The serving eNB may receive the CQI from the UE and may schedule the UEfor data transmission on assigned resources, which may include all or asubset of the resources covered by the power decision pilots from theneighbor eNBs. The serving eNB may then send a downlink (DL) grant anddata transmission in accordance with the reported CQI to the UE at timeT₄. The UE may receive and decode the data transmission from the servingeNB. The UE may send acknowledgement (ACK) if the data transmission isdecoded correctly or negative acknowledgement (NACK) if the datatransmission is decoded in error at time T₅.

In the design shown in FIG. 2, the serving eNB may transmit a PDPtrigger to initiate transmission of power decision pilots by neighboreNBs. In another design, the UE may transmit a PDP request to initiatetransmission of power decision pilots by the neighbor eNBs. Powerdecision pilots may also be transmitted in other manners. For example,the eNBs may transmit power decision pilots periodically, without anytrigger or request.

In one design, the serving eNB may transmit the PDP trigger, the pilot,and data in subframes of one interlace for the downlink. This interlacemay include subframes that are spaced apart by Q subframes, where Q maybe equal to 4, 6, 8 or some other value. The UE may transmit the PDPrequest, the CQI, and the ACK/NACK in subframes of one interlace for theuplink. This design may simplify transmission of data and feedbackinformation. In another design, the various transmissions may be sent inpredetermined or configurable subframes.

FIG. 3 shows a design of an uplink data transmission scheme 300 thatuses power decision pilots. A UE may have data to send to a serving eNBand may transmit a resource request at time T₀. The serving eNB mayobserve high interference from other UEs, and may transmit a PDP requestat time T₁ to ask the other UEs to transmit power decision pilots. TheUE may also receive PDP requests from neighbor eNBs. Each UE maydetermine the transmit power level that it can use on subsequenttime-frequency resources in response to one or more PDP requestsreceived from one or more eNBs. Each UE may transmit a power decisionpilot, at time T₂, which may indicate the transmit power level that theUE can use on the subsequent time-frequency resources.

The serving eNB may receive the power decision pilots from the UE aswell as other UEs. The serving eNB may estimate SNR based on thereceived power decision pilots. The serving eNB may generate an uplinkgrant, which may include assigned resources, a selected MCS, a transmitpower level to use on the assigned resources, etc. The serving eNB maysend the uplink grant to the UE at time T₃. The UE may receive theuplink grant and may send data transmission in accordance with theuplink grant at time T₄. The serving eNB may receive and decode the datatransmission from the UE and may send ACK or NACK based on the decodingresult at time T₅.

In one design, the serving eNB may transmit the PDP request, the uplinkgrant, and ACK/NACK in subframes of one interlace for the downlink. TheUE may transmit the resource request, the power decision pilot, and datain subframes of one interlace for the uplink. This design may simplifytransmission of data and feedback information. In another design, thevarious transmissions may be sent in predetermined or configurablesubframes.

As shown in FIG. 2, power decision pilots may be transmitted by eNBs tosupport data transmission on the downlink. As shown in FIG. 3, powerdecision pilots may be transmitted by UEs to support data transmissionon the uplink. In one design, a power decision pilot may be transmittedin response to a PDP request. In another design, a power decision pilotmay be transmitted in accordance with a configuration, which may specifywhen, where, and how many times to transmit the power decision pilot. Apower decision pilot may be transmitted in various manners, as describedbelow.

LTE utilizes orthogonal frequency division multiplexing (OFDM) on thedownlink and single-carrier frequency division multiplexing (SC-FDM) onthe uplink. OFDM and SC-FDM partition a frequency range into multiple(N_(FFT)) orthogonal subcarriers, which are also commonly referred to astones, bins, etc. Each subcarrier may be modulated with data. Ingeneral, modulation symbols are sent in the frequency domain with OFDMand in the time domain with SC-FDM. The spacing between adjacentsubcarriers may be fixed, and the total number of subcarriers (N_(FFT))may be dependent on the system bandwidth. For example, N_(FFT) may beequal to 128, 256, 512, 1024 or 2048 for system bandwidth of 1.25, 2.5,5, 10 or 20 megahertz (MHz), respectively.

FIG. 4 shows a frame structure 400 used for frequency division duplexing(FDD) in LTE. The transmission timeline for each of the downlink anduplink may be partitioned into units of radio frames. Each radio framemay have a predetermined duration (e.g., 10 milliseconds (ms)) and maybe partitioned into 10 subframes with indices of 0 through 9. Eachsubframe may include two slots. Each radio frame may thus include 20slots with indices of 0 through 19. Each slot may include L symbolperiods, e.g., seven symbol periods for a normal cyclic prefix (as shownin FIG. 4) or six symbol periods for an extended cyclic prefix. The 2Lsymbol periods in each subframe may be assigned indices of 0 through2L-1. On the downlink, an OFDMA symbol may be sent in each symbol periodof a subframe. On the uplink, an SC-FDMA symbol may be sent in eachsymbol period of a subframe.

On the downlink in LTE, an eNB may transmit a primary synchronizationsignal (PSS) and a secondary synchronization signal (SSS) in the center1.08 MHz of the system bandwidth for each cell served by the eNB. ThePSS and SSS may be transmitted in symbol periods 6 and 5, respectively,in subframes 0 and 5 of each radio frame with the normal cyclic prefix,as shown in FIG. 4. The PSS and SSS may be used by the UEs for cellacquisition. The eNB may transmit a Physical Broadcast Channel (PBCH) insymbol periods 0 to 3 in slot 1 of subframe 0 in certain radio frames.The PBCH may carry some system information.

An eNB may transmit one or more power decision pilots on the downlinkwith OFDMA. Some time-frequency resources may be selected fortransmitting the power decision pilot(s) and may be distributed acrosstime and frequency. OFDMA symbols may be generated with the powerdecision pilot(s) transmitted on the selected time-frequency resources.

FIG. 5 shows a design of transmitting one or more power decision pilotson the downlink with OFDMA. The available time frequency resources forthe downlink may be partitioned into resource blocks. A resource blockmay cover 12 subcarriers in one slot, and a pair of resource blocks maycover 12 subcarriers in one subframe. Each resource block may include anumber of resource elements. Each resource element may cover onesubcarrier in one OFDMA symbol period and may be used to send onemodulation symbol, which may be a real or complex value.

In one design, certain resource blocks may be used to transmit one ormore power decision pilots and may be referred to as selected resourceblocks. The selected resource blocks may be located in subframes thatare spaced apart by K subframes, where K may be one or greater. K may beselected based on time variation in a wireless channel. A smaller valueof K may be used for high time variation, and a larger value of K may beused for low time variation.

The selected resource blocks may occupy multiple sets of subcarriersacross frequency to capture frequency variation in the wireless channel.In one design, the selected resource blocks may occupy different sets ofsubcarriers in different subframes, e.g., as shown in FIG. 5. Thesedifferent sets of subcarriers may be selected based on astaggering/hopping pattern. In another design, the selected resourceblocks may occupy the same sets of subcarriers across subframes (notshown in FIG. 5).

In general, a sufficient number of resource elements may be used totransmit a power decision pilot to enable accurate SNR estimation whilereducing overhead due to the power decision pilot. The selected resourceelements may be distributed across time and frequency to capture timeand frequency variations in the wireless channel. The selected resourceelements may be located in certain symbol periods, or certain slots, orcertain subframes, etc. The selected resource elements may be staggeredacross frequency (which may improve performance in a synchronousnetwork) or may be fixed across frequency (which may be more desirablein an asynchronous network). The power decision pilot may be transmittedon a set of resource elements, which may be selected in various manners.

FIG. 6A shows a design of a subframe format 610 for transmitting a powerdecision pilot on the downlink in a pair of resource blocks with OFDMA.As shown in FIG. 6A, a subframe may include a control zone followed by adata zone. The control zone may include the first M OFDMA symbol periodsof the subframe, where M may be equal to 1, 2, 3 or 4 in general and M=3in FIG. 6A. M may change from subframe to subframe. Control informationmay be transmitted in the first M OFDMA symbols. The data zone mayinclude the remaining 2L−M OFDMA symbol periods of the subframe and maycarry data for UEs.

Subframe format 610 in FIG. 6A may be used by an eNB equipped with twoantennas. A cell-specific reference signal may be transmitted on someresource elements in symbol periods 0, 4, 7 and 11 and may be used bythe UEs for channel estimation and other measurements. A power decisionpilot may be transmitted on a set of resource elements, which may beselected from among the resource elements in the data zone that are notused for the cell-specific reference signal. In the design shown in FIG.6A, the set of resource elements includes all resource elements in theresource block pair in symbol periods 3 and 8. This design can capturehigh frequency variation and low time variation.

FIG. 6B shows a design of a subframe format 620 for transmitting a powerdecision pilot on the downlink in a pair of resource blocks with OFDMA.In the design shown in FIG. 6B, the set of resource elements used forthe power decision pilot includes every third resource elements in theresource block pair in symbol periods 3, 6, 9 and 12. This design cancapture moderate frequency variation and moderate time variation.

FIGS. 6A and 6B show two exemplary designs for transmitting a powerdecision pilot on a pair of resource blocks in a subframe. The resourceelements used for transmitting the power decision pilot may also beselected based on other patterns. In general, more resource elements maybe selected across frequency to capture frequency variation, and moreresource elements may be selected across time to capture time variation.The number of resource elements to use for the power decision pilot maybe selected based on a tradeoff between SNR accuracy and pilot overhead.The specific resource elements to use for the power decision pilot maybe selected from among the resource elements available for transmittingdata, which may reduce impact due to the power decision pilot. Theresource elements to use for the power decision pilot may avoid thecontrol zone, the cell-specific reference signal, the PSS and SSS, andother control channels and reference signals.

A power decision pilot may be transmitted on a set of resource elementsin various manners. In one design, a sequence of modulation symbols maybe generated based on a pseudo-random sequence. In another design, asequence of modulation symbols may be generated based on a CAZAC(constant amplitude zero auto correlation) sequence having a flatspectral response and zero auto-correlation. Some exemplary CAZACsequences include a Zadoff-Chu sequence, a Chu sequence, a Franksequence, a generalized chirp-like (GCL) sequence, etc. For bothdesigns, the modulation symbols in the sequence may be mapped to theresource elements used to transmit the power decision pilot. OFDMAsymbols may be generated with (i) the modulation symbols for the powerdecision pilot mapped to the resource elements used to transmit thepower decision pilot and (ii) other modulation symbols and/or zerosymbols with zero signal value mapped to other resource elements. In onedesign, the sequence of modulation symbols may uniquely identify atransmitter of the power decision pilot and/or may convey otherinformation. A receiver may know the identity of the transmitter and maybe able to generate the sequence of modulation symbols in the samemanner as the transmitter.

In one design, different eNBs may transmit their power decision pilotson the same time-frequency resources, e.g., the same set of resourceelements. The power decision pilots from different eNBs would thenoverlap one another, which may simplify SNR estimation by the UEs.Furthermore, an eNB may skip transmitting its power decision pilot onthe time-frequency resources if the eNB will not transmit data onsubsequent time-frequency resources. The UEs can receive all powerdecision pilots on the same time-frequency resources and can measure thepower decision pilots from all eNBs that will transmit on the subsequenttime-frequency resources. In another design, different eNBs may transmittheir power decision pilots on different time-frequency resources. Thisdesign may be especially applicable for an asynchronous network and/ormay be used for other reasons.

In one design, a transmit power level for a power decision pilot may beset equal to a transmit power level for data transmission on subsequenttime-frequency resources, so that P_(PDP)=P_(DATA). This design maysimplify SNR estimation by the UEs. This design may also allow an eNB toskip transmitting the power decision pilot (or equivalently, to transmitthe power decision pilot at zero transmit power) to indicate that theeNB will not transmit on subsequent time-frequency resources. In anotherdesign, the transmit power level for the power decision pilot may be setequal to a scaled version of the transmit power level for datatransmission, so that P_(PDP)=α×P_(DATA), where α is a scaling factorthat may be known by both the eNB and the UEs. In yet another design,the power decision pilot may be transmitted at a fixed power level, andthe transmit power level for data transmission may be conveyed byinformation sent in the power decision pilot.

In one design, an eNB may transmit a single power decision pilot toindicate a transmit power level that the eNB will use for datatransmission across the entire system bandwidth in a future subframe.The eNB may transmit this power decision pilot across frequency, e.g.,as shown in FIG. 5.

FIG. 7A shows a design of transmitting multiple power decision pilotsfor different subbands. The system bandwidth may be partitioned into Ssubbands that may be assigned indices of 1 through S, where S may be oneor greater. Each subband may cover 1.08 MHz or some other range offrequencies. In one design, an eNB may transmit a power decision piloton each of the S subbands. In this design, the power decision pilottransmitted on subband s may indicate the transmit power level that theeNB will use for data transmission on subband s in a future subframe,where sε{1, . . . , S}. In another design, the eNB may transmit powerdecision pilots on only a subset of the S subbands. In this design, thepower decision pilot on a given subband may indicate the transmit powerlevel that the eNB will use for data transmission on that subband aswell as one or more other subbands.

FIG. 7B shows another design of transmitting multiple power decisionpilots for different subbands. In this design, an eNB may transmit thepower decision pilots for all subbands on a designated subband, whichmay be subband 1 (as shown in FIG. 7B) or some other subband. Each powerdecision pilot may indicate the transmit power level that the eNB willuse for data transmission on one or more subbands associated with thatpower decision pilot.

FIG. 7C shows a design of transmitting multiple power decision pilotsfor different subframes. In this design, an eNB may transmit multiplepower decision pilots to indicate the transmit power levels that it willuse for data transmission in different subframes. For example, the eNBmay transmit multiple power decision pilots in subframe t. One powerdecision pilot may indicate the transmit power level that the eNB willuse for data transmission in subframe t+Q, another power decision pilotmay indicate the transmit power level that the eNB will use for datatransmission in subframe t+Q+1, etc., where Q may be one or greater.

The designs in FIGS. 7A and 7B may allow an eNB to convey the transmitpower levels that it will use for data transmission in the future withfiner resolution across frequency. The design in FIG. 7C may allow theeNB to convey the transmit power levels that it will use for datatransmission in the future with finer resolution across time.

In general, an eNB may transmit multiple power decision pilots toindicate transmit power levels that the eNB will use for datatransmission on different sets of subsequent time-frequency resources,which may be in different subbands and/or different subframes. The eNBmay transmit these power decision pilots in various manners, e.g., asshown in FIG. 7A, 7B or 7C. In one design, the eNB may transmit themultiple power decision pilots on different sets of resource elements inthe same resource block(s). This design may reduce the number ofresource blocks used for the power decision pilots, which may thenreduce the number of resource blocks not available for datatransmission. In another design, the eNB may transmit the multiple powerdecision pilots on different sets of resource elements in differentresource blocks. In yet another design, the eNB may transmit multiplepower decision pilots on the same set of resource elements, and thepower decision pilots may be distinguished with different scramblingcodes.

A UE may transmit one or more power decision pilots on the uplink withSC-FDMA. Some time-frequency resources may be selected for transmittingthe power decision pilot(s). SC-FDMA symbols may be generated with thepower decision pilot(s) transmitted on the selected time-frequencyresources.

As noted above, modulation symbols are transmitted in the time domainwith SC-FDMA. In a given SC-FDMA symbol period, N modulation symbols maybe sent on N subcarriers by (i) performing an N-point discrete Fouriertransform (DFT) on the N modulation symbols to obtain N frequency-domainsymbols, where N may be an integer multiple of 12 for LTE, (ii) mappingthe N frequency-domain symbols to the N subcarriers used fortransmission, (iii) mapping zero symbols to the remaining subcarriers,(iv) performing an N_(FFT)-point inverse fast Fourier transform (IFFT)on N_(FFT) mapped symbols for the N_(FFT) subcarriers to obtain N_(FFT)time-domain samples, and (v) appending a cyclic prefix to the N_(FFT)samples to obtain an SC-FDMA symbol. It may be desirable to transmit themodulation symbols on N consecutive subcarriers in order to obtain alower peak-to-average-power ratio (PAPR) for an SC-FDMA waveform.

FIG. 8 shows a design of transmitting a power decision pilot on theuplink in one resource block with SC-FDMA. A 2-dimensional block 800 maybe used to denote the time-frequency resources available for oneresource block with SC-FDMA. The horizontal axis may represent time andmay be partitioned into units of SC-FDMA symbol periods. The verticalaxis may also represent time and may be partitioned into units of symbollocations. Twelve symbol locations may be available for one resourceblock and may be assigned indices of 0 through 11. Block 800 may includea number of resource units. Each resource unit may cover one symbollocation in one SC-FDMA symbol period and may be used to send onemodulation symbol.

A power decision pilot may be transmitted on a set of resource units inone or more resource blocks. In the design shown in FIG. 8, the powerdecision pilot is transmitted in each SC-FDMA symbol period. In anotherdesign, the power decision pilot may be transmitted in only some SC-FDMAsymbol periods in a slot.

In one design, a power decision pilot may be transmitted in apredetermined fraction or percentage of the resource units available ineach SC-FDMA symbol period in which the power decision pilot istransmitted. This predetermined fraction may be denoted as p and may bebetween 0 and 1, or 0<p≦1. In the example shown in FIG. 8, p=⅙ and thepower decision pilot may be transmitted in two out of 12 resource unitsin each SC-FDMA symbol period.

In one design, a power decision pilot may be transmitted in the samesymbol locations across SC-FDMA symbol periods, e.g., in symbollocations 10 and 11 in each SC-FDMA symbol period for the example shownin FIG. 8. In another design, a power decision pilot may be transmittedin different symbol locations across SC-FDMA symbol periods. In thisdesign, the symbol locations for the power decision pilot may beselected based on a staggering/hopping pattern.

In general, a power decision pilot may be transmitted in a sufficientnumber of resource units to enable accurate SNR estimation whilereducing pilot overhead. The power decision pilot may be transmitted inSC-FDMA symbol periods that may be spaced across time to capture timevariation in the wireless channel. The power decision pilot may betransmitted in contiguous symbol locations to reduce aliasing effects,which may smear modulation symbols across symbol locations.

In one design, different UEs may transmit their power decision pilots tooverlap one another. This may be achieved by having each UE transmit itspower decision pilot with the same predetermined fraction p as well asin the same part of the available symbol locations, as described below.

FIG. 9 shows a design of transmitting power decision pilots on theuplink by four UEs in one SC-FDMA symbol period. In the example shown inFIG. 8, p=⅓ and each UE may transmit its power decision pilot in thelast ⅓ of the symbol locations available for that UE in the SC-FDMAsymbol period. In the example shown in FIG. 9, UE #1 is allocated fourresource blocks covering 48 symbol locations with indices of 0 through47. UE #2 is allocated two resource blocks covering 24 symbol locationswith indices of 0 through 23. UE #3 is allocated one resource blockcovering 12 symbol locations with indices of 0 through 11. UE #4 isallocated three resource blocks covering 36 symbol locations withindices of 0 through 35.

In the example shown in FIG. 8, UE #1 transmits data in symbol locations0 through 31 and transmits a power decision pilot in symbol locations 32through 47. UE #2 transmits data in symbol locations 0 through 15 andtransmits a power decision pilot in symbol locations 16 through 23. UE#3 transmits nothing in symbol locations 0 through 7 and transmits apower decision pilot in symbol locations 8 through 11. UE #4 transmitsdata in symbol locations 0 through 23 and does not transmit a powerdecision pilot in symbol locations 24 through 35, e.g., because UE #4will not transmit on subsequent time-frequency resources.

FIG. 10 shows plots of the transmissions from the four UEs in FIG. 9. InFIG. 10, the horizontal axis represents time and covers one SC-FDMAsymbol period. The vertical axis represents transmit power. As shown inFIG. 10, both UE #1 and UE #2 transmit data in the first ⅔ of theSC-FDMA symbol period and transmit their power decision pilots in thelast ⅓ of the SC-FDMA symbol period. UE #3 transmits its power decisionpilot in the last ⅓ of the SC-FDMA symbol period. UE #4 transmits datain the first ⅔ of the SC-FDMA symbol period. As shown in FIG. 10, thepower decision pilots from all UEs overlap in the last ⅓ of the SC-FDMAsymbol period due to transmission of the power decision pilot with thesame predetermined fraction p as well as on the same part of theavailable symbol locations in the SC-FDMA symbol period.

FIGS. 9 and 10 show a design in which the UEs use the same fraction p=⅓of the available symbol locations for the power decision pilots andfurther transmit their power decision pilots in contiguous symbollocations. This design may result in overlapping power decision pilots(e.g., as shown in FIG. 10), which may simplify SNR estimation. Ingeneral, the UEs may transmit their power decision pilots with the sameor different fractions of the available symbol locations. Furthermore,the UEs may transmit their power decision pilots in contiguous ornon-contiguous symbol locations.

In another design, a UE may transmit data and a power decision pilotwith time division multiplexing (TDM). In this design, one or moreSC-FDMA symbol periods may be used to transmit the power decision pilot,and the remaining SC-FDMA symbol periods may be used to transmit dataand/or other information. The UE may transmit the power decision piloton all available resource units in each SC-FDMA symbol period selectedfor transmitting the power decision pilot.

In yet another design, a UE may transmit data and a power decision piloton different sets of subcarriers. For example, the UE may be assignedone or more resource blocks in a first subband for data transmission andmay need to transmit the power decision pilot on one or more resourceblocks in a second subband. The UE may frequency division multiplexeddata with the power decision pilot. The UE may generate an SC-FDMAsymbol comprising data on a first set of subcarriers in the firstsubband and the power decision pilot on a second set of subcarriers inthe second subband. Since the first and second sets of subcarriers arenot contiguous, the UE would not maintain a single-carrier waveform forthe SC-FDMA symbol.

A UE may transmit multiple power decision pilots in a given SC-FDMAsymbol period. These power decision pilots may indicate the transmitpower levels that the UE will use for data transmission on differentsubbands and/or in different subframes. The UE may transmit the multiplepower decision pilots in various manners.

In one design, the UE may time division multiplexed the multiple powerdecision pilots in different sets of symbol locations in the sameSC-FDMA symbol period. For example, if p=⅓, then the UE may transmit afirst power decision pilot in the first ⅓ symbol locations, transmit asecond power decision pilot in the next ⅓ symbol locations, etc. Thisdesign may allow the UE to transmit multiple power decision pilots fordifferent subbands and/or different subframes in a single subband, e.g.,as shown in FIG. 7B. This design may allow the UE to maintain asingle-carrier waveform.

In another design, the UE may time division multiplexed multiple powerdecision pilots in different SC-FDMA symbol periods. For example, the UEmay transmit a first power decision pilot in a first SC-FDMA symbolperiod of a slot or subframe, transmit a second power decision pilot ina second SC-FDMA symbol period of the slot or subframe, etc. This designmay allow the UE to transmit multiple power decision pilots fordifferent subbands and/or different subframes in a single subband.

In yet another design, the UE may frequency division multiplexed themultiple power decision pilots on different sets of subcarriers, e.g.,in different subbands. For example, the UE may transmit a first powerdecision pilot on a first set of subcarriers in a first subband,transmit a second power decision pilot on a second set of subcarriers ina second subband, etc., as shown in FIG. 7A. The UE may transmit themultiple power decision pilots on different sets of subcarriers usingSC-FDMA or OFDMA.

A UE may transmit a power decision pilot on a set of resource units inone or more SC-FDMA symbols in various manners. In one design, asequence of modulation symbols may be generated, e.g., based on apseudo-random sequence or a CAZAC sequence. The sequence of modulationsymbols may uniquely identify the UE and/or may convey otherinformation. The modulation symbols in the sequence may be mapped to theresource units used to transmit the power decision pilot. One or moreSC-FDMA symbols may be generated with (i) the modulation symbols for thepower decision pilot mapped to the resource units used to transmit thepower decision pilot and (ii) other modulation symbols and/or zerosymbols mapped to remaining resource units.

In one design, a transmit power level for a power decision pilot may beset equal to a transmit power level for data transmission on subsequenttime-frequency resources. In another design, the transmit power levelfor the power decision pilot may be set equal to a scaled version of thetransmit power level for data transmission. In yet another design, thepower decision pilot may be transmitted at a fixed power level, and thetransmit power level for data transmission may be conveyed byinformation sent in the power decision pilot.

For both the downlink and uplink, a power decision pilot may betransmitted in various manner spatially. In one design, a power decisionpilot may be transmitted without precoding. In another design, a powerdecision pilot may be transmitted in a particular spatial direction withprecoding. In yet another design, multiple power decision pilots may betransmitted corresponding to multiple layers that may be used for datatransmission. The power decision pilots for the multiple layers may ormay not overlap.

FIG. 11 shows a design of a process 1100 for transmitting a powerdecision pilot. Process 1100 may be performed by a station, which may bea base station/eNB, or a UE, or some other entity. The station maydetermine a set of time-frequency resources to use for transmitting apower decision pilot (block 1112). This set of time-frequency resourcesmay include a fraction of time-frequency resources available fortransmission. In one design, the station may determine a transmit powerlevel for the power decision pilot based on a transmit power level touse for data transmission (block 1114). The transmit power level for thepower decision pilot may be equal to the transmit power level for datatransmission, or related to the transmit power level for datatransmission by a scaling factor, or equal to a fixed transmit powerlevel.

The station may transmit the power decision pilot on the set oftime-frequency resources in a first time period, at the transmit powerlevel determined for the power decision pilot, to indicate the transmitpower level to use for data transmission in a second time period afterthe first time period (block 1116). The station may transmit the powerdecision pilot at zero power if data transmission will not be sent inthe second time period. In one design, the first and second time periodsmay correspond to consecutive subframes in an interlace that includesevenly spaced subframes. In another design, the second time period maybe separated from the first time period by a variable amount, which maybe conveyed by the power decision pilot or via some other mechanism.

In one design, the station may receive a request to transmit a powerdecision pilot and may transmit the power decision pilot in response tothe request. In another design, the station may receive an indication totransmit the power decision pilot in accordance with a particularconfiguration. The station may then periodically transmit the powerdecision pilot in accordance with the configuration, e.g., in evenlyspaced time periods.

In one design, the station may transmit the power decision pilot withOFDMA. In this design, the set of time-frequency resources may comprisea set of resource elements, which may include a fraction of resourceelements available for transmission. The set of resource elements may bedistributed across a plurality of subcarriers and/or a plurality ofsymbol periods in at least one resource block, e.g., as shown in FIG. 6Aor 6B. The station may transmit the power decision pilot on the set ofresource elements. The station may generate at least one OFDMA symbolcomprising the power decision pilot on the set of resource elements andmay transmit the at least one OFDMA symbol. The power decision pilot maybe transmitted on the same subcarriers in different OFDMA symbols or ondifferent subcarriers in different OFDMA symbols. The differentsubcarriers may be determined based on a staggering/hopping pattern.

In another design, the station may transmit the power decision pilotwith SC-FDMA. In this design, the set of time-frequency resources maycomprise a set of resource units in at least one SC-FDMA symbol. The setof resource units may include a predetermined fraction of all resourceunits available for transmission in each SC-FDMA symbol, e.g., as shownin FIG. 8. The set of resource units may also comprise predeterminedones of the available resource units, e.g., the last two resource unitsin each SC-FDMA symbol, as shown in FIG. 8. The station may generate atleast one SC-FDMA symbol comprising the power decision pilot in the setof resource units and may transmit the at least one SC-FDMA symbol. Thepower decision pilot may be transmitted in the same symbol locations indifferent SC-FDMA symbols (e.g., as shown in FIG. 8) or in differentsymbol locations in different SC-FDMA symbols.

In one design, the station may generate a sequence of symbolsidentifying the station. The station may map the sequence of symbols tothe set of time-frequency resources to use for transmitting the powerdecision pilot. A plurality of stations may transmit their powerdecision pilots on the same set of time-frequency resources. The powerdecision pilots from these stations would then overlap, which maysimplify SNR estimation.

In one design, the station may transmit the power decision pilot on asubband among a plurality of subbands. The power decision pilot mayindicate the transmit power level to use for data transmission on thesame subband in the second time period.

In one design, the station may determine a second set of time-frequencyresources to use for transmitting a second power decision pilot. Thestation may transmit the second power decision pilot on the second setof time-frequency resources in the first time period to indicate asecond transmit power level to use for data transmission after the firsttime period. In one design, for OFDMA, the two sets of time-frequencyresources for the two power decision pilots may comprise two sets ofresource elements in at least one resource block. In another design, forSC-FDMA, the two sets of time-frequency resources may comprise two setsof resource units in the same SC-FDMA symbol or in different SC-FDMAsymbols.

In one design, the two power decision pilots may be transmitted on firstand second subbands and may indicate the transmit power levels to usefor data transmission on the first and second subbands, respectively,e.g., as shown in FIG. 7A. In another design, the two power decisionpilots may be transmitted on the same subband and may indicate thetransmit power levels to use for data transmission on the first andsecond subbands, e.g., as shown in FIG. 7B. In yet another design, thetwo power decision pilots may be transmitted in the first time periodand may indicate transmit power levels to use for data transmission inthe second time period and a third time period. The station may alsotransmit one or more additional power decision pilots.

FIG. 12 shows a design of an apparatus 1200 for transmitting a powerdecision pilot. Apparatus 1200 includes a module 1212 to determine a setof time-frequency resources to use for transmitting a power decisionpilot, a module 1214 to determine a transmit power level for the powerdecision pilot based on a transmit power level to use for datatransmission, and a module 1216 to transmit the power decision pilot onthe set of time-frequency resources in a first time period to indicatethe transmit power level to use for data transmission in a second timeperiod after the first time period.

FIG. 13 shows a design of a process 1300 for receiving power decisionpilots. Process 1300 may be performed by a first station, which may be abase station/eNB, or a UE, or some other entity. The first station mayreceive at least one power decision pilot from at least one interferingstation on a set of time-frequency resources in a first time period(block 1312). Each power decision pilot may indicate a transmit powerlevel to use for data transmission in a second time period after thefirst time period by an interfering station transmitting the powerdecision pilot.

The first station may estimate channel quality in the second time periodbased on the at least one power decision pilot received in the firsttime period (block 1314). In one design, the first station may estimateinterference due to each interfering station in the second time periodbased on the power decision pilot received from that interferingstation. The first station may then estimate channel quality in thesecond time period based on the estimated interference from the at leastone interfering station.

The first station may send information indicative of the estimatedchannel quality to a second station (block 1316). The first station maythen receive data transmission sent by the second station in the secondtime period based on the information (block 1318). For data transmissionon the downlink, the first station may be a UE, the second station maybe a serving base station, and the at least one interfering station maybe at least one interfering base station. For data transmission on theuplink, the first station may be a base station, the second station maybe a target UE, and the at least one interfering station may be at leastone interfering UE.

FIG. 14 shows a design of an apparatus 1400 for receiving power decisionpilots. Apparatus 1400 includes a module 1412 to receive at least onepower decision pilot from at least one interfering station on a set oftime-frequency resources in a first time period at a first station, amodule 1414 to estimate channel quality in the second time period basedon the at least one power decision pilot received in the first timeperiod, a module 1416 to send information indicative of the estimatedchannel quality from the first station to a second station, and a module1418 to receive data transmission sent by the second station in thesecond time period based on the information.

The modules in FIGS. 12 and 14 may comprise processors, electronicdevices, hardware devices, electronic components, logical circuits,memories, software codes, firmware codes, etc., or any combinationthereof.

FIG. 15 shows a block diagram of a design of a base station/eNB 110 anda UE 120, which may be one of the base stations/eNBs and one of the UEsin FIG. 1. Base station 110 may be equipped with T antennas 1534 athrough 1534 t, and UE 120 may be equipped with R antennas 1552 athrough 1552 r, where in general T≧1 and R≧1.

At base station 110, a transmit processor 1520 may receive data from adata source 1512 and control information from a controller/processor1540. Processor 1520 may process (e.g., encode, interleave, and symbolmap) the data and control information to obtain data symbols and controlsymbols, respectively. Processor 1520 may also generate pilot symbolsfor one or more power decision pilots and reference signals. A transmit(TX) multiple-input multiple-output (MIMO) processor 1530 may performspatial processing (e.g., precoding) on the data symbols, the controlsymbols, and/or the pilot symbols, if applicable, and may provide Toutput symbol streams to T modulators (MODs) 1532 a through 1532 t. Eachmodulator 1532 may process a respective output symbol stream (e.g., forOFDM, etc.) to obtain an output sample stream. Each modulator 1532 mayfurther process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal. Tdownlink signals from modulators 1532 a through 1532 t may betransmitted via T antennas 1534 a through 1534 t, respectively.

At UE 120, antennas 1552 a through 1552 r may receive the downlinksignals from base station 110 and may provide received signals todemodulators (DEMODs) 1554 a through 1554 r, respectively. Eachdemodulator 1554 may condition (e.g., filter, amplify, downconvert, anddigitize) its received signal to obtain input samples. Each demodulator1554 may further process the input samples (e.g., for OFDM, etc.) toobtain received symbols. A MIMO detector 1556 may obtain receivedsymbols from all R demodulators 1554 a through 1554 r, perform MIMOdetection on the received symbols if applicable, and provide detectedsymbols. A receive processor 1558 may process (e.g., demodulate,deinterleave, and decode) the detected symbols, provide decoded data forUE 120 to a data sink 1560, and provide decoded control information to acontroller/processor 1580.

On the uplink, at UE 120, a transmit processor 1564 may receive andprocess data from a data source 1562 and control information fromcontroller/processor 1580. Processor 1564 may also generate pilotsymbols for one or more power decision pilots and reference signals. Thesymbols from transmit processor 1564 may be precoded by a TX MIMOprocessor 1566 if applicable, further processed by modulators 1554 athrough 1554 r (e.g., for SC-FDM, etc.), and transmitted to base station110. At base station 110, the uplink signals from UE 120 may be receivedby antennas 1534, processed by demodulators 1532, detected by a MIMOdetector 1536 if applicable, and further processed by a receiveprocessor 1538 to obtain decoded data and control information sent by UE120. Processor 1538 may provide the decoded data to a data sink 1539 andthe decoded control information to controller/processor 1540.

Controllers/processors 1540 and 1580 may direct the operation at basestation 110 and UE 120, respectively. Channel processors 1546 and 1584may process power decision pilots and other pilots received on theuplink and downlink, respectively, and may obtain channel qualityestimates. Processor 1540 and/or other processors and modules at basestation 110 may perform or direct process 1100 in FIG. 11, process 1300in FIG. 13, and/or other processes for the techniques described herein.Processor 1580 and/or other processors and modules at UE 120 may alsoperform or direct process 1100, process 1300, and/or other processes forthe techniques described herein. Memories 1542 and 1582 may store dataand program codes for base station 110 and UE 120, respectively. Ascheduler 1544 may schedule UEs for data transmission on the downlinkand/or uplink.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method for wireless communication, comprising:transmitting, by an apparatus, to a second apparatus, a power decisionpilot trigger; determining a set of time-frequency resources to use fortransmitting a power decision pilot, the set of time-frequency resourcesincluding a fraction of time-frequency resources available fortransmission; transmitting, by the apparatus, to the second apparatus,the power decision pilot on the set of time-frequency resources in afirst time period to indicate a transmit power level to be used by theapparatus for data transmission in a second time period after the firsttime period, wherein transmitting the power decision pilot comprisestransmitting a sequence of modulation symbols generated based on apseudo-random sequence; receiving, by the apparatus, from the secondapparatus, channel quality information (CQI), wherein the CQI is basedon the power decision pilot and further based on a second power decisionpilot from an interfering third apparatus, and wherein the CQI isreceived in response to the power decision pilot trigger; andtransmitting, by the apparatus, to the second apparatus, data inaccordance with the CQI.
 2. The method of claim 1, further comprising:determining a transmit power level for the power decision pilot based onthe transmit power level to use for data transmission in the second timeperiod, wherein the power decision pilot is transmitted at the transmitpower level determined for the power decision pilot.
 3. The method ofclaim 1, wherein the power decision pilot is transmitted at zero powerif data transmission is not sent in the second time period.
 4. Themethod of claim 1, wherein the determining the set of time-frequencyresources comprises determining a set of resource elements to use fortransmitting the power decision pilot, and wherein the transmitting thepower decision pilot comprises transmitting the power decision pilot onthe set of resource elements.
 5. The method of claim 4, wherein the setof resource elements is distributed across a plurality of subcarriersand a plurality of symbol periods in at least one resource block.
 6. Themethod of claim 4, wherein the transmitting the power decision pilot onthe set of resource elements comprises generating at least oneOrthogonal Frequency Division Multiple Access (OFDMA) symbol comprisingthe power decision pilot on the set of resource elements, andtransmitting the at least one OFDMA symbol.
 7. The method of claim 1,wherein the determining the set of time-frequency resources comprisesdetermining a set of resource units to use for transmitting the powerdecision pilot in at least one Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) symbol, and wherein the transmitting the powerdecision pilot comprises transmitting the power decision pilot on theset of resource units in the at least one SC-FDMA symbol.
 8. The methodof claim 7, wherein the set of resource units occupies a predeterminedfraction of symbol locations available for transmission in each SC-FDMAsymbol.
 9. The method of claim 7, wherein the set of resource unitscomprises predetermined ones of resource units available fortransmission in the at least one SC-FDMA symbol.
 10. The method of claim7, wherein the transmitting the power decision pilot comprises:generating the at least one SC-FDMA symbol comprising the power decisionpilot on the set of resource units, and transmitting the at least oneSC-FDMA symbol.
 11. The method of claim 1, wherein the transmitting thepower decision pilot comprises: generating a sequence of symbolsidentifying a station transmitting the power decision pilot, and mappingthe sequence of symbols to the set of time-frequency resources to usefor transmitting the power decision pilot.
 12. The method of claim 1,wherein the power decision pilot is transmitted in a particular spatialdirection.
 13. The method of claim 1, wherein the power decision pilotis transmitted on a subband among a plurality of subbands and indicatesthe transmit power level to use for data transmission on the subband inthe second time period.
 14. The method of claim 1, wherein a pluralityof stations transmit overlapping power decision pilots on the set oftime-frequency resources.
 15. The method of claim 1, further comprising:determining a second set of time-frequency resources to use fortransmitting a second power decision pilot; and transmitting the secondpower decision pilot on the second set of time-frequency resources inthe first time period to indicate a second transmit power level to usefor data transmission after the first time period.
 16. The method ofclaim 15, wherein the set of time-frequency resources comprises a firstset of resource elements in at least one resource block, and wherein thesecond set of time-frequency resources comprises a second set ofresource elements in the at least one resource block.
 17. The method ofclaim 15, wherein the set of time-frequency resources comprises a firstset of resource units in at least one Single-Carrier Frequency DivisionMultiple Access (SC-FDMA) symbol, and wherein the second set oftime-frequency resources comprises a second set of resource units in theat least one SC-FDMA symbol.
 18. The method of claim 15, wherein the setof time-frequency resources comprises a first set of resource units in afirst Single-Carrier Frequency Division Multiple Access (SC-FDMA) symbolin a subframe, and wherein the second set of time-frequency resourcescomprises a second set of resource units in a second SC-FDMA symbol inthe subframe.
 19. The method of claim 15, wherein the power decisionpilot is transmitted on a first subband and indicates the transmit powerlevel to use for data transmission on the first subband, and wherein thesecond power decision pilot is transmitted on a second subband andindicates the second transmit power level to use for data transmissionon the second subband.
 20. The method of claim 15, wherein the powerdecision pilot is transmitted on a first subband and indicates thetransmit power level to use for data transmission on the first subband,and wherein the second power decision pilot is transmitted on the firstsubband and indicates the second transmit power level to use for datatransmission on a second subband.
 21. The method of claim 15, whereinthe second power decision pilot indicates the second transmit powerlevel to use for data transmission in a third time period after thesecond time period.
 22. The method of claim 1, further comprising:receiving a request to transmit the power decision pilot, and whereinthe power decision pilot is transmitted in response to receiving therequest.
 23. The method of claim 1, wherein the power decision pilot istransmitted periodically in evenly spaced time periods.
 24. The methodof claim 1, wherein the power decision pilot is transmitted on differentsubcarriers in different time periods based on a pattern.
 25. The methodof claim 1, wherein the first time period and the second time periodcorrespond to consecutive subframes in an interlace including evenlyspaced subframes.
 26. An apparatus for wireless communication,comprising: means for transmitting, by the apparatus, to a secondapparatus, a power decision pilot trigger; means for determining a setof time-frequency resources to use for transmitting a power decisionpilot, the set of time-frequency resources including a fraction oftime-frequency resources available for transmission; means fortransmitting, by the apparatus, to the second apparatus, the powerdecision pilot on the set of time-frequency resources in a first timeperiod to indicate a transmit power level to be used by the apparatusfor data transmission in a second time period after the first timeperiod, wherein transmitting the power decision pilot comprisestransmitting a sequence of modulation symbols generated based on apseudo-random sequence; means for receiving, by the apparatus, from thesecond apparatus, channel quality information (CQI), wherein the CQI isbased on the power decision pilot and further based on a second powerdecision pilot from an interfering third apparatus, and wherein the CQIis received in response to the power decision pilot trigger; and meansfor transmitting, by the apparatus, to the second apparatus, data inaccordance with the CQI.
 27. The apparatus of claim 26, furthercomprising: means for determining a transmit power level for the powerdecision pilot based on the transmit power level to use for datatransmission in the second time period, wherein the power decision pilotis transmitted at the transmit power level determined for the powerdecision pilot.
 28. The apparatus of claim 26, wherein the means fordetermining the set of time-frequency resources comprises means fordetermining a set of resource elements to use for transmitting the powerdecision pilot, and wherein the means for transmitting the powerdecision pilot comprises means for transmitting the power decision piloton the set of resource elements.
 29. The apparatus of claim 26, whereinthe means for determining the set of time-frequency resources comprisesmeans for determining a set of resource units to use for transmittingthe power decision pilot in at least one Single-Carrier FrequencyDivision Multiple Access (SC-FDMA) symbol, and wherein the means fortransmitting the power decision pilot comprises means for transmittingthe power decision pilot on the set of resource units in the at leastone SC-FDMA symbol.
 30. The apparatus of claim 26, wherein the means fortransmitting the power decision pilot comprises: means for generating asequence of symbols identifying a station transmitting the powerdecision pilot, and means for mapping the sequence of symbols to the setof time-frequency resources to use for transmitting the power decisionpilot.
 31. An apparatus for wireless communication, comprising: at leastone processor configured to transmit, by the apparatus, to a secondapparatus, a power decision pilot trigger, determine a set oftime-frequency resources to use for transmitting a power decision pilot,the set of time-frequency resources including a fraction oftime-frequency resources available for transmission, transmit, by theapparatus, to the second apparatus, the power decision pilot on the setof time-frequency resources in a first time period to indicate atransmit power level to be used by the apparatus for data transmissionin a second time period after the first time period, whereintransmitting the power decision pilot comprises transmitting a sequenceof modulation symbols generated based on a pseudo-random sequence,receive, by the apparatus, from the second apparatus, channel qualityinformation (CQI), wherein the CQI is based on the power decision pilotand further based on a second power decision pilot from an interferingthird apparatus, and wherein the CQI is received in response to thepower decision pilot trigger, and transmit, by the apparatus, to thesecond apparatus, data in accordance with the CQI.
 32. The apparatus ofclaim 31, wherein the at least one processor is configured to determinea transmit power level for the power decision pilot based on thetransmit power level to use for data transmission in the second timeperiod, and to transmit the power decision pilot at the transmit powerlevel determined for the power decision pilot.
 33. The apparatus ofclaim 31, wherein the at least one processor is configured to determinea set of resource elements to use for transmitting the power decisionpilot, and to transmit the power decision pilot on the set of resourceelements.
 34. The apparatus of claim 31, wherein the at least oneprocessor is configured to determine a set of resource units to use fortransmitting the power decision pilot in at least one Single-CarrierFrequency Division Multiple Access (SC-FDMA) symbol, and to transmit thepower decision pilot on the set of resource units in the at least oneSC-FDMA symbol.
 35. The apparatus of claim 31, wherein the at least oneprocessor is configured to generate a sequence of symbols identifying astation transmitting the power decision pilot, and to map the sequenceof symbols to the set of time-frequency resources to use fortransmitting the power decision pilot.
 36. A computer program product,comprising: a non-transitory computer-readable medium comprising: codefor causing the at least one computer to transmit, by an apparatus, to asecond apparatus, a power decision pilot trigger; code for causing theat least one computer to determine a set of time-frequency resources touse for transmitting a power decision pilot, the set of time-frequencyresources including a fraction of time-frequency resources available fortransmission; code for causing the at least one computer to transmit, bythe apparatus, to the second apparatus, the power decision pilot on theset of time-frequency resources in a first time period to indicate atransmit power level to be used by the apparatus for data transmissionin a second time period after the first time period, whereintransmitting the power decision pilot comprises transmitting a sequenceof modulation symbols generated based on a pseudo-random sequence; codefor causing the at least one computer to receive, by the apparatus, fromthe second apparatus, channel quality information (CQI), wherein the CQIis based on the power decision pilot and further based on a second powerdecision pilot from an interfering third apparatus, and wherein the CQIis received in response to the power decision pilot trigger; and codefor causing the at least one computer to transmitting, by the apparatus,to the second apparatus, data in accordance with the CQI.
 37. A methodfor wireless communication, comprising: receiving, at a first station,from a second station, a power decision pilot trigger; transmitting, bythe first station, a power decision pilot request to at least oneinterfering station; receiving, in response to the power decision pilotrequest, at least one power decision pilot from the at least oneinterfering station on a set of time-frequency resources in a first timeperiod at the first station, wherein each power decision pilot indicatesa transmit power level to use for data transmission in a second timeperiod after the first time period by an interfering stationtransmitting the power decision pilot; estimating channel quality in thesecond time period based on the at least one power decision pilotreceived in the first time period; sending information indicative of theestimated channel quality from the first station to the second station;and receiving data transmission at the first station sent by the secondstation in the second time period based on the information.
 38. Themethod of claim 37, wherein the estimating channel quality comprises:estimating interference due to each of the at least one interferingstation in the second time period based on the power decision pilotreceived from the interfering station in the first time period, andestimating channel quality in the second time period based on estimatedinterference from the at least one interfering station in the secondtime period.
 39. The method of claim 37, wherein the first station is auser equipment (UE), the second station is a serving base station, andthe at least one interfering station is at least one interfering basestation.
 40. The method of claim 37, wherein the first station is a userequipment (UE), the second station is a serving base station, and the atleast one interfering station is at least one interfering base station.41. An apparatus for wireless communication, comprising: means forreceiving, at a first station, from a second station, a power decisionpilot trigger; means for transmitting, by the first station, a powerdecision pilot request to at least one interfering station; means forreceiving, in response to the power decision pilot request, at least onepower decision pilot from the at least one interfering station on a setof time-frequency resources in a first time period at the first station,wherein each power decision pilot indicates a transmit power level touse for data transmission in a second time period after the first timeperiod by an interfering station transmitting the power decision pilot;means for estimating channel quality in the second time period based onthe at least one power decision pilot received in the first time period;means for sending information indicative of the estimated channelquality from the first station to the second station; and means forreceiving data transmission at the first station sent by the secondstation in the second time period based on the information.
 42. Theapparatus of claim 41 wherein the means for estimating channel qualitycomprises: means for estimating interference due to each of the at leastone interfering station in the second time period based on the powerdecision pilot received from the interfering station in the first timeperiod, and means for estimating channel quality in the second timeperiod based on estimated interference from the at least one interferingstation in the second time period.
 43. An apparatus for wirelesscommunication, comprising: at least one processor configured to:receive, at a first station, from a second station, a power decisionpilot trigger; transmit, by the first station, a power decision pilotrequest to at least one interfering station; receive, in response to thepower decision pilot request, at least one power decision pilot from theat least one interfering station on a set of time-frequency resources ina first time period at the first station, wherein each power decisionpilot indicates a transmit power level to use for data transmission in asecond time period after the first time period by an interfering stationtransmitting the power decision pilot; estimate channel quality in thesecond time period based on the at least one power decision pilotreceived in the first time period; send information indicative of theestimated channel quality from the first station to the second station;and receive data transmission at the first station sent by the secondstation in the second time period based on the information.
 44. Theapparatus of claim 43, wherein the at least one processor is configuredto estimate interference due to each of the at least one interferingstation in the second time period based on the power decision pilotreceived from the interfering station in the first time period, and toestimate channel quality in the second time period based on estimatedinterference from the at least one interfering station in the secondtime period.
 45. A computer program product, comprising: anon-transitory computer-readable medium comprising: code for receiving,at a first station, from a second station, a power decision pilottrigger; code for transmitting, by the first station, a power decisionpilot request to at least one interfering station; code for receiving,in response to the power decision pilot request, at least one powerdecision pilot from the at least one interfering station on a set oftime-frequency resources in a first time period at the first station,wherein each power decision pilot indicates a transmit power level touse for data transmission in a second time period after the first timeperiod by an interfering station transmitting the power decision pilot;code for estimating channel quality in the second time period based onthe at least one power decision pilot received in the first time period;code for sending information indicative of the estimated channel qualityfrom the first station to the second station; and code for receivingdata transmission at the first station sent by the second station in thesecond time period based on the information.